In an article on The Motley Fool, Tim Beyers summarizes the reasons why XBRL is good for investors.  The section "What is Buffett buying now?" shows one of the potential uses of XBRL beyond the financial statements.  Forms Forms 4, 13-D, 13F-HR and 13F-NT in XBRL would offer functionality similar to the SEC's executive compensation viewer, which makes use of XBRL.